Retarding field oscillators



June 4, 1957 B. c. GARDNER 2,794,931

RETARDING FIELD OSCILLATORS Filed April 8, 1952 2 Sheets-Sheet 1 V I I L 20 p 20 F76. 28

F'IG. IN VENTOI? BER/MRO C. GARDNER ATTOR EV June 4, 1957 B. c. GARDNER RETARDING FIELD OSCILLATORS 2 Sheets-Sheet 2 Filed April 8, 1952 HTTOIP/VEY United States Patent 2,794,931 i- 'EARDING. FIELD .OSCILLATOR'S "BernardCIGardner, Los Altos, Calif ass'ignorto Raytheon Manufacturing Gm'pany,"New'tou,Mass a corporation of- Delaware -Application April-8,r1952, Serial N0..2s1,o91

- -Claims. (Cl. '313- 85) Thisinventionrelates to retarding-fieldoscillators and,

more-particularly, to; the repeller electrode structure in such oscillators.

By retarding field oscillators is-meant oscillatorsvof .-the type described byHeil and Ebers in-an article entitled Anew widezrange high-frequency oscillator, in thesIune'1950-issueof. the- ProceedingsUof thejIRE, at pages 645-650. Oscillators ofthis type; are clearly 'dis- .ting-uished from velocity-modulated oscillators of :the

reflex type utilizing -the tubes commonlyjknown as reflex .klystrons ina-second'article by Ebers, entitled Retarding field oscillators in the February i 1952. issuerof the same .publicatiombeginning .on page 138 and especially at page .141. .Briefiy, in thereflex klystron theselectrons'are velocitymiodulated in the concentric radio-frequency field betweenzthea-node and the. grid. They then drift and bunch in the repeller. region and return to do work in the radio-frequency field. In the Heil type of tube, the electrons are velocity-modulated by the concentrated radio-frequency field near the nozzle-shaped anode. They then :drift and bunch in a relatively weak radio-frequency field and return to do work on the strong radio-frequency field. In.this.process,-the electronbeam isexpanded or contracted in thenozzle area or just beyond depending on the phase of the oscillation. The return beam will have periodic;:density tvariations whichnterrdcto modulate the outward-going beam; in such a way as to deliver energy to the oscillating circuit.

The repeller electrode in such an oscillator is a-tube which, for-wide band operation, will, in cooperation-with the anode-produceamore or less uniform field. The beam ofelectrons willbe projected up into the "repeller tube, more or less-depending upon the phase ofthe oscillation,but'since'thefield is uniform over narrow ranges of penetration-there-will be a rather uniform focusing condition throughout the cycle.

The invention consists in modifying the repeller structure of such an oscillator so that either a spike of conductive material protrudes from a transverse plane of conductive material within the repeller tube in the direction of the oncoming electron beam, or there are openings formed in the end of the repeller tube nearest the anode. With either repeller construction, a very non-uniform focusing field is obtained within the repeller tube. The electrons entering this field, in a phase which causes them to penetrate further in, will tend to be defocused on the back trip more than those entering in the opposite phase. Consequently, the modulation will be greater and there will be more activity permitting greater eificiency in operation. The structure can be modified to operate efiicient- 1y over a wide range of frequency by arranging the spike so that it is not moved as the tube is moved. The same effect can be obtained by applying a voltage to the spike that can be varied independently of the voltage applied to the repeller tube. With this arrangement, the voltage may be adjusted to an optimum value for the particular wave length to which the oscillator is adjusted.

iPsienied June 4, 1957 2 1 The foregoing and: other; advantages, objects, .and-features of the invention will-bebetter. understood: from-the following f description. taken in conjunction i with the ac- ;companying :drawings wherein:

"Fig. .IHisadOngitudinaI crosssection of :oneembodir ment of the invention;

- -spheroid:cathode: 11 heated by a: coil 12. Electrons'emitted, from the cathode 11 are accelerated toward and through.an -annular'conical opening'13 in the wall of the resonant cavity resonator 14rwhich concentrates the electronslinto a narrow. beam and projects them intoa hollow cylindrical repeller electrode designated 1 generally by: :the

- reference numeral. 15

The construction of this electrode can best'be seen in :Fig. 3. It is, constructed. of a tube16 of insulating material with a coating 17 of conductive material on the outside thatextends into the interior. The tube 16 is mounted so as to be electrically'isolatedfor direct current from the wall of the.opening 18 in thecavity resonator 14but coupled capacitively to the cavity resonator at radio? frequency through a virtual short :circuit. The repeller tube 16 is arranged to bei'moved with respect to the opening 13 for tuning purposes.v This is accomplished by attaching a: (1520 tothe end of.v the tube 16, and passing it through the envelopev 10 by means of abellows 21; that permits-the rod2l) to.be moved'inreither of the directions indicatedby the-arrows 122 and-23while retaining the vacuum-within the .envelope10. If it is desired to maintainthe rod-24 at axpotential' different from that of the:surface 17'of.the tube.'1 6, the rod is mounted in a manner to insulateit from the tube 16. The rod 214 is formed with aaspikei 25-at the end. nearest the opening 13.

With the: mounting .shown in. Big. 1, the rod 24 remains in positionwhilethe tube 116 isrmove'd. A terminal "26 isiformed .ontthe' end: of v the rod 124'to connect itto -'a .source' of; potential.

The, potentialsepplied to thevariouselectrodes can best be seen from the schematic diagram of Fig. 2. A source 27 of-negativegpotential is connected betweenthe cathode 11 and the cavity resonator 14, the positive terminal of a second source 28 of potential is connected to the cavity resonator 14 and a tap 29 is connected to the repeller tube 16. The rod 24 is connected to a second tap 30 on the source of negative potential 28. This is an optional connection to enable the repeller tube 16 and the rod 24 to be maintained at dilferent potentials that can be independently adjusted. If this is not desired, the rod 24 and tube 16 may be connected together to the source 28.

The effect of the spike 25 upon the operation of the oscillator is best understood by reference to Fig. 3. It will be seen that the beam of electrons 31 is emitted from the cathode 11 and concentrated by the anode 13. The electrostatic field between the repeller 15 and the anode 13 is represented by the equipotential lines 32, shown dotted. It will be seen that the electron stream 31 splits as it approaches the spike 25 and returns to the outside of the anode 13. The dotted lines 32 show that the electrostatic field in this region is not uniform. As a result, the electrons entering this field, in a phase which causes them to penetrate further in, will tend to be defocused on the back trip more than those entering in the opposite phase. This modulation will be greater than that which .would be produced if the spike were not present. This greater modulation results in more activity and in more efficient operation.

The range over which the oscillatorcan be operated with reasonable efficiency can be extended by maintaining the rod 24 stationary as the distance of the repeller tube 16 from the anode 13 is varied to vary the capacity between the elements, thus varying the resonant frequency of the cavity resonator14.

The same objective can be achieved by establishing a potential on the rod 24 that is independent of the potential on the surface 17 of the tube 16. This independent potential can then be adjusted to give the best result at each operating frequency over a wide range,

Figs. 4 and 5 show how these efiects may be obtained by another construction of the repeller electrode. The repeller tube 33' is formed with a main section 34, and a second short concentric section 35 of the same diameter connected to the main section. by a plurality of rods 36 arranged with their axes parallel to that of the repeller tube 33 and in the cylindrical surface of the tube. The effect of the openings between the rods 36 is to distort the focused field in much the same manner as the arrangement shown in Fig. 3. The resulting field is shown bythe equipotential lines 37, shown dotted. The same effect can be obtained by slots cut into the walls of the repeller tube 33.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled .in the art.

What is claimed is:

1.A retarding field oscillator comprising a cathode formed with a hemispherical concave surface, a conical annular accelerating electrode having tapered inner edges forming a focussing electrical field in this region, and a repeller. electrode disposed along a common axis, said repeller electrode comprising a hollow cylindrical member, and means near the end of the repeller nearest the accelerating electrode to distort the focusing field.

2. A retarding field oscillator comprising a cathode, a conical annular accelerating electrode having tapered inner edges forming a focussing electrical field in this region, and a repeller electrode disposed along a common axis, said repeller electrode comprising a hollow cylindrical member, and means near the end of repeller nearest the accelerating electrode to distort the focusing field, said means comprising openings in the walls of the repeller electrode.

3. A retarding field oscillator comprising a cathode formed with a hemispherical concave surface, a conical annular accelerating electrode having tapered inner edges forming a focussing electrical field in this region, and a repeller electrode disposed along a common axis, said repeller electrode comprising a hollow cylindrical mem-.

her, and means near the end of the repeller nearest the accelerating electrode to distort the focusing field, said means comprising conductive material disposed within the repeller electrode in a plane transverse to the electron stream and a conductive rod projecting from the said plane toward the accelerating electrode parallel to the electron stream.

4. A retarding field oscillator comprising a cathode formed with a hemispherical concave surface, a conical annular accelerating electrode having tapered inner edges forming a focussing electrical field in this region, and a repeller electrode disposed along a common axis, said repeller electrode comprising a hollow cylindrical mem-:

her, and means near the end of the repeller nearest the accelerating electrode to distort the focusing field, said means comprising conductive material disposed within the repeller electrode in a plane transverse to the electron stream and a conductive rod projecting from the said plane toward the accelerating electrode parallel to the. electron stream, and means to cause relative motion between said rod and said cylindrical repeller electrode.

5. A retarding field oscillator comprising a cathode formed with a hemispherical concave surface, a conical annular accelerating electrode having tapered inner edges forming a focussing electrical field in this region, and a repeller electrode disposed along a common axis, said repeller electrode comprising a hollow cylindrical member, and means near the end of the repeller nearest the accelerating electrode to distort the focusing field, said means comprising conductive material disposed within the repeller electrode in a plane transverse to the elec-.

tron stream and a conductive rod projecting from the said plane toward the accelerating electrode parallel to the electron stream, and means to maintain the repeller electrode and the rod at separate potentials negative with respect to that of the accelerating electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,913 Pierce et al. Dec. 3, 1946 2,513,359 Pierce July 4, 1950 2,513,277 Best July 4, 1950 2,523,031 Laiferty Sept. 19, 1950 2,593,443 Harrison .Apr. 22, 1952 2,631,258 Gardner Mar. 10, 1953 2,651,738 Ebers Sept. 8, 1953 

